The present invention relates to an apparatus for sensing whether a vehicle seat is in a reference position. More particularly, the present invention relates to an apparatus for sensing position of a rail member of a vehicle seat relative to a bracket member of the vehicle seat.
It is often desirable to know a position of a vehicle seat. For example, in a vehicle with a vehicle occupant protection device, such as an air bag, determined or sensed position of the seat may be used to determine control of the protection device.
A known seat position sensing apparatus includes a permanent magnet for producing a magnetic field and a Hall effect device for sensing the magnetic flux of the magnetic field. When a rail member of the vehicle seat is located in a position adjacent the apparatus, the flux density of the magnetic field increases. The Hall effect device senses the increased flux density. The increased flux density is indicative of a forward position of the vehicle seat.
Foreign ferrous materials that are introduced into the magnetic field may change the flux density of the magnetic field resulting in an inaccurate reading of the vehicle seat position. Examples of foreign ferrous material that may be present near the magnetic field of the known apparatus on a vehicle seat include paper clips, foil wrappers, ink pens, coins, etc.
The present invention is an apparatus for sensing when a rail member of a vehicle seat is located in a reference position relative to a seat bracket of the vehicle seat. The apparatus comprises a magnetic sensor for generating a magnetic field and for sensing a flux density of the magnetic field. The apparatus further comprises a cover for enclosing the magnetic sensor. The cover, when in a first position, forms a zone for preventing the flux density from increasing above a threshold level. The cover is moved into a second position when the rail member is located in the reference position relative to the seat bracket. In the second position, the flux density is increased above the threshold level.